1. Technical Field
The present invention embodiments pertain to determining locations of emitters. In particular, the present invention embodiments pertain to determining locations of radio frequency (RF) emitters based on lines-of-bearing at various locations to the emitters.
2. Discussion of Related Art
Conventional techniques for direction finding (DF), i.e., determining a line-of-bearing (LOB), and geolocation of a radio frequency (RF) emitter are commonly based on measurements of a received signal strength (RSS) of signals transmitted from the emitter. The received signal strength (RSS) is usually integrated over the duration of the transmitted signal in order to obtain a signal energy measurement and enhance signal to noise ratio. Since the transmitted radio frequency (RF) signal attenuates during propagation through space, the received signal strength (RSS) of the signal may be used to estimate the distance from the receiver to the emitter. However, this technique may not be very accurate due to multipath fading, shadowing effects, and path loss modeling errors that may significantly distort the expected received signal strength (RSS).
Furthermore, conventional line-of-bearing (LOB) intersection based geolocation techniques are all based on least-squares (LS) approaches to solve over-determined linear and non-linear equations. However, the LS based approaches often provide biased estimates and are computationally expensive.
In order to improve the accuracy, the conventional line-of-bearing (LOB) and geolocation techniques may employ a radio frequency (RF) propagation map of the environment. The map is basically a database with information created from known terrain data and learned from observed energy measurements at different combinations of emitter and receiver locations. The improved geolocation technique determines the best fit in the energy space to potential emitter locations based on the radio frequency (RF) propagation map. However, this improved technique requires a large number of real-time measurements and/or terrain modeling. Thus, this technique can only be used in applications in which the radio frequency (RF) propagation map is available, and sufficient computing capacity exists to process the large amount of data.